Fixed docker.md for PE
Fixed docker.md for PE

volodymyr-babak/thingsboard.github.io,thingsboard/thingsboard.github.io,thingsboard/thingsboard.github.io,thingsboard/thingsboard.github.io,volodymyr-babak/thingsboard.github.io,thingsboard/thingsboard.github.io,volodymyr-babak/thingsboard.github.io,volodymyr-babak/thingsboard.github.io